Early reports suggest that a bird strike caused a jet plane to crash in theHudson River near Manhattan today, leaving questions about how a little flyinganimal could down a big airliner.

More than 200 people have been killedworldwide as a result of wildlife strikes with aircraft since 1988, according toBird Strike Committee USA, and more than 5,000 bird strikes were reported by theU.S. Air Force in 2007. Bird strikes, or the collision of an aircraftwith an airborne bird, tend to happen when aircraft are close to the ground,which means just before landing or after take-off, when jet engines are turningat top speeds.

The incidents are serious particularly when the birds,usually gulls, raptors and geese, are sucked into a jet engine and strikean engine fan blade. That impact displaces the blade such that it strikesanother blade and a cascade can occur, resulting in engine failure.

Today's incident, which occurred just after USAirways flight 1549 (an Airbus 320) had taken off with more than 150 passengersand crew members from LaGuardia Airport in New York, en route to Charlotte,N.C., involved a flock of geese, according to CBS News. Reports indicate nodeaths or serious injuries as of this writing.

Large aircraft are certifiedto be able to keep flying after impacting a 4-pound bird, however 36 species of birdsin North America weigh more than this, according to the committee. Evensmaller birds, such as starlings, can cause engine failure.

The greater thedifference in the speed of the plane and the bird, the greater the force of theimpact on the aircraft. The weight of the bird is also a factor, but the speeddifference is a much bigger factor.

Flocks of birds are even more dangerousas they can result in multiple strikes.Delicate birds, delicate aircraftDale Oderman, associate professor of aviation technology at PurdueUniversity in Indiana says birds can be very dangerous to aircraft, particularlyin the first several thousand feet after take-off, where the birds are flying.

"Obviously, geese or another large bird would be much more hazardous than alittle black bird," Oderman said. "The speed at which the two are moving causesthe bird to get ingested into the engine. And the engine is very delicate towithstanding a major impact."

He added: "It just shuts the engine down."

Basically, if thebirds get too close to the engine's intake, it's like a vacuum - the birdsjust get sucked in.

"The initial stages of a jet engine are made up of a lotof compressor blades. Those aren't very big and they can be very easilydamaged," Oderman told LiveScience. "Even if one of those things breaks off,then the one blade will go through the rest of the engine and it's like shrapnelto the engine."

And in the case of the Hudson River crash, the birdsapparently took out both engines.

"Apparently in this particular case itseems both engines were hit. If it was a flock of birds they flew thought itwouldn't be a surprise to me," Oderman said.

Airports, Oderman said, takeseveral precautions to keep planes safe from birds. For instance, they oftendon't plant many trees nearby, as these are nesting areas for birds. Since LaGuardia is right on the water, he noted, there are a lot of water birds around.

Bird strike remains

Bird strikes are on the rise, according to thecommittee. After a bird strike in the United States, the remains, called snarge,are sent to the Smithsonian Institution's Feather Identification Laboratory toidentify the species, according to WikiPedia.

Bird and other wildlifestrikes to aircraft result in more than $600 million in damage a year, accordingto Bird Strike Committee USA. Five jet airliners have had major accidentsinvolving bird strikes since 1975, the committee says. In one case, about threedozen people died.

NASA worries about bird strikes, too.

During the July2005 launch of Discovery on mission STS-114, a vulture soaring around the launchpad impacted the shuttle's external tank just after liftoff. With a vulture'saverage weight ranging from 3 to 5 pounds, a strike at a critical point on theshuttle - like the nose or wing leading thermal protection panels - could causecatastrophic damage to the vehicle.

NASA put safetymeasures into place in 2005 to reduce the odds of bird strikes with theshuttle. The agency particularly wants to avoid bird strikes to the shuttle'sfuel tank that could damage the heat shield during launch and landing.

Forinstance, NASA has a special during launch countdown where they can stop to waitfor birds to pass. And during landing, NASA has a sound cannon that they fire tomake sure the runway is clear from birds to make sure shuttle isn't damagedduring landing.